A Manual of the Chemistry of the Carbon Compounds

THE CARBON COMPOUNDS. 173
Solid fatty acids maybe separated from each other by fractional
precipitation. The mixture is dissolved in spirits of wine, and an
alcoholic solution of lead acetate or magnesium acetate is added in
small quantities, by which the acids having the highest molecular
weight are first precipitated. To the filtrate again a small quantity
of the lead or magnesium salt is added, and this operation repeated
until all the acids are precipitated. The different precipitates are
decomposed with hydrochloric acid, and if necessary again treated in
the same way until pure acids are obtained. The purity of an acid
thua separated is easily recognized by subjecting it again to fractional
precipitation ; when pure, the first precipitate yields an acid having
the same composition and melting-point as that obtained from the
last precipitate.
Pure acids melt and solidify at the same temperature, whilst the
melting-point of a mixture is not only always lower than that of the
most fusible constituent, but the temperature at which it again
solidifies is always lower than tliat at which it melts. Thus the
melting-point of stearic acid is 69'2°, and that of palmitic acid 62°,
whilst a mixture consisting of 30 parts of stearic acid and 70 parts
of palmitic acid melts at 55"'l, and solidifies apiin at 54°.
Laurie Acid C12HMO occurs in the fat contained in the berries of
the bay-tree (Launis ndbilis), in pichuriin beans, and also in cocoa-nut
oil. It forms white needles melting at 43 O# 6.
Myrislic Acid CMHM0o is found in nutmeg butter, in spermaceti,
and other fats. It crystallizes in white needles melting at 53 O# 8.
Palmitic Add OlflH32Oa is one of the chief constituents of the
different kinds of tallow, of spermaceti, palm oil, olive oil, and a
great number of other fats. It is best obtained from palm-oil soap, a
mixture of sodium palmitate and stearate, hy dissolving it in alcohol
and separating the acids by fractional precipitation.
Palmitic acid crystallizes in shining scales and melts at 62°.
Margaric Acid CqH»Ov—This name was originally given to an
acid supposed to exist in several fata, but it has since been shown
that the so-called margaric acid is only a mixture of palmitic and
stearic acids. Mnrgaric acid does not appear to exist in natural
fats, but has been produced artificially by heating cetyl iodide
with potassium cyanide, and decomposing the margaronitrile thus
fomea with alcoholic potash. It has^ great resemblance to palmitic
acid.
Stearic Acid CLHggOj occurs, together with palmitic acid and other
acids, in suet, tallow, cocoa-nut oil, cocoa butter, in human fat, in
the fat of the goose, &c. &c. It is easily obtained from tallow-soap
by dissolving it in six parts of hot water, and adding to the solution
40—50 parts of cold water. A mixture of acid sodium stearate and
]ialmitate separates in shining scales. On crystallizing this mix hire
from hot alcohol the steainte separates first, and may bo purified by
recrystallization. On decomposing this salt t.y hydrochloric acid,
and reciystallizing the nciil from hot nlculm] it is obtained in nacreous